The rule change you associate with Gretzky was really driven by the Edmonton Oilers as a team -- not Gretzky in particular. And I'd make the case that he had less of an impact on that rule change than two of his teammates: Paul Coffey and Jari Kurri. The NHL changed that rule because those two players (in particular) were dominant on the open ice in a 4-on-4 situation, and the Oilers would use that to their advantage by trying to get coincidental penalties to force 4-on-4 play. That's why the NHL changed the rule.
Interesting point of trivia regarding Edmonton: During their prime in the 1980s they would have SIX future Hall of Famers playing on their top power play unit. Grant Fuhr was in goal, Gretzky played center, and Coffey played on one point. Mark Messier -- who centered their second line -- moved up and played left wing on this unit. Glenn Anderson, who played right wing on that second line, moved up to play right wing on the power play. And first-line right winger Jari Kurri moved back and played the other point next to Coffey. That was an amazing team. Their 446 goals in the 1983-84 season (more than 5.5 goals per game) is a record that may never be matched. That 1983-84 team is probably a close #2 to the 1976-77 Montreal Canadiens as the greatest team in NHL history.
I treasure the first time I took my son to Edmonton to watch 99 and the Oilers play. A wonderful lady working for the Oilers, Shelia McKaskell, thought it so extraordinary someone would travel that far to see the team, we ended up in Pocklington’s old seats behind the bench (a few rows), received caps, etc and met Gretzky in the locker room area after the game. Went back in ‘88 for the first two games against Boston, and the next season for Gretzky’s first game back. I have a picture of #99, mullet and all, with my son hanging in my office. Showed a small copy of the photo to #99 and he started laughing at his hair.
Forgot to mention you should definitely read Ken Dryden’s new book “Scotty”. Bowman picks his top 8 teams ever and does a mythical Stanley Cup playoff to determine the greatest team ever. Pretty sure you’ll like the book.
Don’t forget Michael Phelps and Usain Bolt as the most dominant athletes on earth.